This invention relates to electrochemical fuel cells and, more particularly, to fuel cell membrane electrode assemblies and the flow field structures adjacent thereto.
Electrochemical fuel cells generate electrical current through the oxidation of a fuel. One type of fuel cell employs a membrane electrode assembly ("MEA") including a membrane having an anode side and cathode side, depending on the direction of the current with respect thereto. The membrane itself serves as an electrolyte. A suitable catalyst for the electrochemical reaction is applied to the membrane, or is incorporated into the polymeric composition from which the membrane is prepared. Alternatively, the catalyst is applied to carbon fiber paper, which is then laminated to the membrane to form the membrane electrode assembly.
Located on both sides of the MEA is a flow field which typically consists of a graphite plate which has been machined to provide a series of channels on its surface, as shown, for example, in U.S. Pat. Nos. 5,300,370 and 5,230,966. The channels transport fuel to the anode side and oxidant to the cathode side, and transport reaction products primarily from the cathode side, and are typically separated from the membrane electrode assembly by a thin layer of a porous carbon material, such as carbon fiber paper.
U.S. Pat. No. 5,252,410 describes a fuel cell membrane electrode assembly wherein a porous electrically conductive sheet material is used as the flow field. Such flow fields have been used in a MEA configuration where the dispersion of catalyst used in the preparation of the catalyst layer is applied to the porous flow field. In such configurations, adequate performance is only obtained when this catalyst flow field structure is then laminated to the membrane.